1. Field
The present invention relates to a fuel cell unit, a control method thereof, an information processing apparatus, and a power supply control method thereof, and more particularly relates to a fuel cell unit to be connected to an information processing apparatus via a connector, a control method of the fuel cell unit, an information processing apparatus, and a power supply control method thereof.
2. Description of the Related Art
As a secondary battery used as one of electric power supply sources for information processing apparatuses, for example, a lithium ion battery has been currently used. Compared to a disposal type primary battery, as one of features of the secondary battery, it can be repeatedly used when being charged, for example, using a commercial power source.
However, since being a secondary battery, the lithium ion battery must be charged, for example, using a commercial power source.
In addition, improvement in performance of information processing apparatuses has been significant in recent years, and concomitant with this improvement, electric power consumption of the information processing apparatuses tend to be increased. Accordingly, the increase in energy density, that is, an output energy amount per unit volume or per unit mass, of the lithium ion battery which supplies an electric power to information processing apparatuses has been desired; however, it has been difficult to expect remarkable improvement under current circumstances.
On the other hand, it has been said that the energy density of a fuel cell is theoretically 10 times that of the lithium ion battery (for example, see “Fuel Cell 2004 (Nenryou-Denchi 2004)” Nikkei Business Publications, Inc., pp. 49-50 and pp. 64, October 2003, hereinafter referred to as Non Patent Document 1). This means that, when having the same volume or the same mass as that of the lithium ion battery, the fuel cell has a potential ability to supply an electric power for a longer time (such as 10 times). In addition, it also means that when the time of the fuel cell to supply an electric power is equal to that of the lithium ion battery, the fuel cell has a high potential ability to reduce its own size and weight as compared to that of the lithium ion battery.
In addition, when fuel such as methanol is sealed inside a small container which is to be used as a replacement unit, and the small container itself is replaced with new container for the fuel supply, charging performed using an external tool is not required. Hence, for example, when an electric power is ensured by the fuel cell at a place at which AC power supply facilities are not present, an information processing apparatus can be used for a long period of time as compared to the case in which an electric power is ensured by the lithium ion battery.
Furthermore, when an information processing apparatus (such as a notebook type personal computer) using the lithium ion battery is used for a long period of time, it is difficult to perform long-term operation by using an electric power supplied from the lithium ion battery, and hence the use of the information processing apparatus is limited to a circumstance in which the supply of electric power is available from an AC power source. However, compared to the case in which the information processing apparatus is operated using the lithium ion battery, the information processing apparatus can be operated for a long time by using an electric power supplied from the fuel cell, and in addition, it can be expected that the limitation described above is resolved.
From the points described above, for the purpose of supplying an electric power to information processing apparatuses, research and development of the fuel cell has been carried out and has also been disclosed, for example, in Japanese Patent Application Publication (KOKAI) No. 2003-142137 and Japanese Patent Application Publication (KOKAI) No. 2002-169629.
Although various fuel cell systems (for example, see “Everything of Fuel Cell (Nenryoudenchi-no-subete),” Hironosuke Ikeda, Nippon Jitsugyo Publishing Co., Ltd., August 2001, hereinafter referred to as Non Patent Document 2) have been proposed, in consideration of compactness, light weight, and easy handling properties of fuel, for example, a direct methanol fuel cell (DMFC) system may be mentioned. This fuel cell system uses methanol as a fuel, and methanol is directly fed to a fuel electrode without being converted into hydrogen.
In the direct methanol fuel cell, the concentration of methanol to be fed to the fuel electrode is important, and when this concentration is high, the power generation efficiency is degraded, and as a result, sufficient performance cannot be obtained. This degradation is caused by a phenomenon (called a cross-over phenomenon) in which part of methanol used as a fuel passes through an electrolyte membrane (solid high molecular weight electrolyte membrane) placed between a fuel electrode (negative electrode) and an air electrode (positive electrode). The cross-over phenomenon becomes apparent when the concentration of methanol is high, and when low concentration methanol is fed to the fuel electrode, the above phenomenon can be suppressed.
On the other hand, when low concentration methanol is used, although high performance is easily ensured, since the fuel volume is increased (such as 10 times) as compared to that of high concentration methanol, the size of a fuel container (fuel cartridge) becomes large.
Accordingly, while high concentration methanol is received in the fuel cartridge to reduce the size thereof, before being fed to the fuel electrode, when methanol is diluted with water which is generated during power generation and is circulated using small pumps, valves and the like to decrease the high concentration methanol, the cross-over phenomenon can be suppressed. By the method described above, the power generation efficiency can be improved. Hereinafter, the pumps, the valves and the like which are used for circulating generated water are collectively called an auxiliary device, and the circulation system as described above is called a dilution circulation system.
As described above, while the size and the weight of the entire fuel cell unit are being reduced, a fuel cell unit having a high power generation efficiency can be realized using diluted methanol (Non-Patent Document 1).
By employing the dilution circulation system in a direct methanol fuel cell, the size and weight of the entire fuel cell unit can be reduced, and in addition, the power generation efficiency can be increased, so that a high-output fuel cell unit can be realized.
However, in the dilution circulation system, the auxiliary device including pumps and valves is necessary for circulating water and the like, and hence a power source for driving the auxiliary device is required. When the fuel cell itself once starts the power generation, the auxiliary device can be driven by an electric power generated thereby; however, at least before the fuel cell itself starts the power generation, a power source for driving the auxiliary device is necessary. Hence, a system may be considered in which a power source (such as a small lithium ion battery) for generating a small electric power is additionally embedded in the fuel cell unit so as to drive the auxiliary device at the start of operation.
Incidentally, in many information processing apparatuses (such as a notebook personal computer), a secondary battery (such as a lithium ion battery) is embedded in order to enable the apparatus to be operated for a predetermined time. Hence, when the auxiliary device is driven by an electric power supplied from the secondary battery embedded in the information processing apparatus at the start of the fuel cell unit, the power supply for the auxiliary device is not necessary for the fuel cell unit side, and as a result, the size and the weight thereof can be further reduced.
When the drive of the auxiliary device is once started, and diluted methanol used as a fuel and air are started to be supplied to the fuel electrode and the air electrode, respectively, the fuel cell unit starts its own power generation. After the fuel cell starts the power generation, when the electric power generated by the fuel cell is supplied to the information processing apparatus, the information processing apparatus is driven, and in addition, part of the electric power can drive the auxiliary device.
In addition, when the electric power is excessively generated, the secondary battery embedded in the information processing apparatus can be charged. When the external fuel cell unit and the secondary battery inside the information processing apparatus are complementarily driven as described above, an optimum power supply system can be provided in which the size and the weight of the system can be reduced as a whole. By the way, this system may be called a hybrid system in some cases.
As described above, a system (that is, the hybrid system) has various advantages in which (1) a fuel cell unit employing the dilution circulation system is connected to an information processing apparatus and (2) without providing a power source inside the fuel cell unit for driving an auxiliary device, an electric power (for driving the auxiliary device or the like) necessary when a fuel cell starts is supplied from a secondary battery embedded in the information processing apparatus.
However, on the other hand, the following problems to be solved may be mentioned. That is,
(1) when a mismatched fuel cell unit or another inadequate unit is connected to the information processing apparatus in order to supply an electric power to the auxiliary device from the secondary battery embedded in the information processing apparatus, the safely of the unit connected to the information processing apparatus as described above cannot be ensured, and in addition, the safety of the information processing apparatus itself may also be impaired in some cases. Hence, in particular, it should be construed that a first problem to be solved is to sufficiently ensure the safety at the start of the operation of the fuel cell unit.
In addition, it is necessary that (2) the auxiliary device be appropriately controlled in accordance with the condition of the fuel cell unit and that of the information processing apparatus. Hence, it should be construed that a second problem to be solved is that the fuel cell unit receives various instructions (commands) from the information processing apparatus when the operation is started, being operated, and stopped.
Accordingly, it is desired that (3) the objects described in the above (1) and (2) can be simply realized at a low cost.